The field of the invention relates to a process commonly used in air conditioning and environmental control systems, namely the spraying or injection of water vapor into an air stream. This lowers the temperature of the air stream by the evaporative cooling effect, while simultaneously raising the relative humidity of the air stream.
A common method has been to use a pump to spray water from a "spray header" consisting of a grouping of nozzles. The spray header is located in the air stream to be treated, the water that is not absorbed by the air stream falls into a pan underneath the spray header, and the unused water in the pan is returned to the suction of the pump. As described in U.S. Pat. Nos. 4,042,016 and 4,118,945, more recently a system has been developed that uses an ultrasonic nozzle, with compressed air as the driving medium, to generate very fine water vapor that is easily evaporated into the air stream.
There are several problems and shortcomings associated with the prior art control and piping systems that have been developed to date, for instance, as illustrated in FIG. 1, to control the amount of compressed air and water to the ultrasonic nozzle. Known control systems commonly use pneumatic control air in order to stage and sequence the various components of the system. This is particularly important when, in order to avoid dripping water after the ultrasonic nozzle is turned off, it is necessary to keep the compressed air running through the nozzle for a period of time after the water has been turned off, so as to clear the lines. This requirement adds to the number of control components.
There are also situations in which no pneumatic control air is available. Therefore, the control system must be electric or electronic. This tends to lead to a greater than desirable number of control relays. As an example, FIG. 2 shows an electrical wiring diagram for a control to supply compressed air and water to the ultrasonic nozzle. The diagram shows the open contacts of the single-pole relays R-1 and R-2, the three pole relay R-3, the time delay single-pole relays TDR-1 and TDR-2, and the air and water solenoids.
The basic sequence of operation of the prior art control system of FIG. 2 is as follows:
1. When the space humidistat calls for humidity, and the various safety controls are electrically closed, the relay R-1 is energized.
2. If the air handling unit fan is running, then the relay R-2 is energized.
3. When the relays R-1 and R-2 are energized, the relay R-3 is powered.
4. As soon as the relay R-3 is powered, the air solenoid opens, thus providing compressed air to the ultrasonic nozzle. After a set period of time, for instance 20 seconds, the time delay relay TDR-1 switches electrically, and the water solenoid opens. At this point the ultrasonic nozzle generates the humidification mist.
5. When humidity is no longer required in the space, the relay R-1 is de-energized. At this point the water solenoid closes immediately, and the air solenoid is held open for a fixed period of time, for instance 20 seconds, by the time delay relay TDR-2, to clear the lines of water and prevent dripping.
This control arrangement requires several electrical components, and a control panel to mount them in.
One of the approaches recently taken to address the problem of water dripping after the water flow stops is to install a three-way valve in the water piping, as shown in FIG. 3. When the water is not required, the valve allows the water to drain from the ultrasonic nozzle, either by gravity or under the compressed air pressure remaining in the ultrasonic nozzle.